1. Field of the Invention
The present invention relates to a method for manufacturing a groove of a substrate and a method for cutting off a substrate. In addition, the present invention relates to a method for manufacturing a semiconductor device. The semiconductor device corresponds to a device including a transistor.
2. Description of the Related Art
In recent years, development of a semiconductor device including a transistor has been advanced. A semiconductor device is formed by forming a transistor over a substrate, and then cutting off the substrate.
In many cases, a substrate is cut off as follows. First, a groove (also referred to as a scribe line) is formed at the surface of the substrate by using a scribing device. Then, the substrate is forcibly cut off along the groove by using a cutting device. In addition, a substrate is cut off by using a laser beam (hereinafter, a laser beam is included in laser light) as follows. First, the substrate is selectively irradiated with a laser beam to locally heat the substrate. Then, the surface of the substrate which is heated is locally cooled by a cooling medium. Subsequently, a crack is formed by utilizing thermal stress which is generated in the substrate, and accordingly, the substrate is cut off (for example, see Patent Document 1)
[Patent Document 1] Japanese Patent Laid-Open No. 2001-64029
When a substrate is cut off by using a scribing device, there is a case where a groove is not formed in a desired shape due to a layer which is provided over the surface of the substrate. As a result, the substrate cannot be cut off in a desired shape, which results in reduction in a yield. In addition, the substrate is cut off by using press power; therefore, a crack is easily generated from the groove and the cutting surface is adversely affected (see a photograph showing a cutting surface of a glass substrate of FIG. 6D). Also, a burr may arise when that the substrate is plastic. “Burr” is called a state that a corner of the substrate is unprocessed smoothly. The state is often beard-form. As described above, cutting off a substrate by using a scribing device has been a factor of generating an exterior problem of a cutting surface and reducing a yield. In addition, it has been difficult to form a scribe line in a polygonal shape or a rounded shape in cutting off a substrate by using a scribing device.
In addition, a cutter is used for a scribing device, and such a cutter becomes worn after using multiple times; therefore, it is necessary that the cutter is replaced. Since a cutter is expensive, it has been difficult to reduce manufacturing cost in using a cutter.
Moreover, when a substrate is cut off by using a laser beam, there are cases where the substrate is transformed due to heating and a crack is generated in the substrate due to stress which remains inside the substrate.